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laid an egg once, the oviduct has bagged oat and shows itself in 

 the following winter like a folded band, rarely straight. So females 

 in their first winter have an oviduct which has not been used and 

 a poorly developed ovary, females in their second winter have the 

 same oviduct and a somewhat stronger developed ovary, older 

 females show an oviduct which has been made use of and their 

 ovary is more or less strongly developed. 



It is not always easy, macroscopically to discern an oviduct which 

 has been used from one which has not been used. In the real winter- 

 months it is sometimes difficult to distinguish the one year old females 

 from elder ones (the ones which have laid eggs) and whereas this is 

 the case in birds of the size of a Guillemot, it is especially the case in 

 all kinds of smaller birds, where the oviduct sometimes is hardly to be 

 found. In such doubtful cases a microscopical examination of sections 

 may give a decisive answer. In the maidenly females the mucosa 

 (taken from about the middle of the oviduct) shows a generally very 

 regular and not very high (often very low) folding; in the females that 

 have laid eggs, the folding is as a rule irregular, untidy and high. 

 This may find its explanation in the fact that the muscular-layer may 

 go back to little more than its former size after the eggs have been laid, 

 may be by contraction, may be by destruction of tissue. The course of 

 this process seems to be very slow: in the Guillemot which surely 

 does not lay any eggs after the middle of August, the oviduct is still 

 distinctly bagged out about the beginning of November and only 

 December-birds show the final situation so that there is a distance of 

 three months or more between egg-laying and the being normal of the 

 oviduct. As the mucosa however is vacant of contracting tissue or such 

 which is being destroyed, it has to fold itself more strongly in propor- 

 tion to the contraction of the muscular layer. It is probably in connec- 

 tion with this last fact that even sections cannot give such a positive 

 answer as one might theoretically expect: some time before the first 

 laying the epitheliumcells of the mucosa begin to increase in number 

 and as this cell-increase sometimes possibly takes place rather early in 

 the bird's bachelor-time, it may be the cause of an early folding which 

 cannot give any surety as to the bird's having laid eggs or not. 



Sections stained with haematoxylin-eosin, gave little trouble in 

 recognizing the oviduct as having been used or not because of the 

 strongly developed bloodvessels in the so called old birds. It seems 

 however that the bloodvessels too already swell some months before the 

 bird's first laying so that, they too, do not give the help one would wish. 

 So by the early development of mucosa and bloodvessels the benefit 

 of the microscopical method may turn out to be of much less impor- 

 tance than I thought at first. 



